Preparation of diborane



\ 46 6 PREPARATION OF DIBORANE,

. mittedto the catalyst container and the container Ralph Klein, Hamden,Herbert GUNadeamlNorthHavehQ y and Louis J. Schoen and Bliss, .NewHaven, Conn., assignors, by mes'ne assignments, to Olin'MathiesonChemical Corporatiomi'arorporation No Drawing. Filed on. s, 1956., Ser.No.-614,768

90mm. (ems-404 This invention relates to a new process for theproduction of diborane, and more particularly to a process for theproduction of diborane by the hydrogenation of trialkylboranes BRRR, thealkyl groups (R, R and R") of which contain from one to five carbonatoms, in the presence of a catalyst selected from metals of group VIIIof the periodic table. I

A number of processes have been advanced in thepast for the productionof diborane. processes was set forth by Stock and Massenez (Stock, A.

and Massenez, C., Berichte, 45, 3529 (1912)). In their process, aspecially prepared magnesium boride is treated with acid to give amixture of boron hydrides fiomwhich by tedious fractionation tetraboranecan be separated. This last named material breaks down under theinfluence of heat to form diborane. This process requires elab- Indhisexperiment 40mg. of palladium black catalyst prepared as describedabovewas added to a standard 105 cc. stainless steel high pressureautoclave or bomb and the bomb was closed. By immersion in a bath cooledwith liquid nitrogen, the bomb and catalyst were cooled to 196 C. andthe bomb was evacuated. Then 2.5 g. of trimethylborane was condensedinto the cold One of the first such the methane formed toescape.

orate apparatus and results, at best, ina very low yield of the desiredproduct.

Another process which has been utilized for the production of diboraneinvolves the reaction of an alkali metal hydride such as lithium hydridewith boron trifluoride in the presence of'diethyl ether. This reaction ialso suifers from several major disadvantages-in that it involves thehandling of a hazardous solvent, diethyl ether, and produces low yieldsof diborane, in the vicinity of 25 percent.

By the process of devised whereby diborane can be produced in good yieldin a reaction involving the use of only hydrogen and a trialkylborane inthe presence of a catalyst which is a metal from the group VIII of theperiodic table. This process can be readily operated and provides ameans whereby substantial quantities of diborane can be produced inconventional apparatus.

The following examples illustrate in detail various embodiment's fallingwithin the scope of this invention.

EXAMPLE I In this experiment trimethylborane (CH B was hydrogenated inthe presence of palladium black catalyst to give diborane.

The palladium black catalyst utilized was prepared in the followingmanner: Two thimbles of pure palladium were dissolved in aqua regia andthe resulting solution was evaporated to dryness. To the 3.32 gm. ofpalladium chloride obtained from the thimbles there was added 1.00 gm.of commercial palladium chloride. In the next step the 4.32 gm. ofpalladium chloride was dissolved in 10.5 ml. of concentrated aqueoushydrochloric acid and 26.5 ml. of water. When solution was complete, 4.2ml. of 37 weight percent formaldehyde solution was added and thesolution made alkaline to litmus with 30 weight percent aqueous sodiumhydroxide solution. The resulting slurry was stirred for five minutesand washed by decantation with ten 100 ml. portions of distilled water.Then the slurry was filtered and the palladium dried in an oven at 80 C.for three hours. Hydrogen at substantially atmospheric pressure wasadstandard stainless steel high pressure autoclave which had beenfiushedwith nitrogen. "Then2.62. g. of trif ethylborane (C H B was poured intothe bomb. The

this invention, a method has been bomb, after which the bomb andcontents were allowed towarmzup to room temperature. The bomb, afterbeing placed in the shaker mechanism, was pressured with hydrogen toapressure of 2,000 p.s.i.g., the shaking mechanism and heater were turnedon, and the bomb was heated to' a temperaturue of 210 C. This reactiontemperature was, maintained for a period of. 12 hours after which thebomb was allowed to cool to room temperature overnight. The contents ofthe bomb were then fvented through a single trap maintained at 'j- 120,C.

Thistrap retained the diborane produced and allowed By infrared and massspectrometer analyses, it was shown that the product contained in the'l20 C. trap was essentially pure diborane and that .the yield ofdiborane was 95 percent.

7 EXAMPLE II Approximately 30 mg. of palladium catalyst prepared asdescribed in Example I was placed in a 105 cc. Arninco triethylboraneutilized was" produced by aGrignard' reaction in which a borontrifiuoride etheratewas prepared and passed into an ether solution ofethyl magnesium bromide. The triethylborane'so produced was identifiedby infrared analysis. During the addition of the triethylborane to thebomb an atmosphere of nitrogen was maintained around the open bomb.After the triethylborane was poured into the bomb, the bomb'was closedand placed in a shaker mechanism. Hydrogen was added to the bomb untilthe pressure gage showed that a pressure of 2100 p.s.i.g. had beenreached. The heater and rocker mechanism were started and in A1, of anhour the bomb reached a temperature of 150 C. which was maintained for12 hours. At the end of the 12 hour period the heater was turned off andthe bomb was allowed to cool to room temperature. It was then attachedto the vacuum rack and the products from. the bomb were passed throughtwo traps both maintained at -l96 C. Non-condensibles were removed fromthe traps by isolating the traps and placing them under vacuum. A whitematerial was condensed in the first trap while only a trace of materialwas to be seen in the second trap. Material in the traps was allowed towarm up to room temperature and a composite sample analyzed by infrared.Infrared showed that the gas was a mixture of diborane and ethane andthat the yield of diborane was approximately percent.

EXAMPLE III In this example 40 mg. of palladium black catalyst preparedas described in Example I was added to the cc. stainless steel bomb.Then 3.7 g. of tri-n-butylborane was poured into the bomb while anatmosphere of nitrogen was maintained around the borane stream IPatented July 26 19 1.0?

placed in the shaker mechanism, closed and pressured up to a pressure of2,000 p.s.i.g. with hydrogen. The shaking mechanism and heater wereturned on and the ranges can also be used. The reaction time can also bevaried widely, but will generally be within the range from 0.5 to 20hours.

It is claimed:

bomb was heated to 200 C.; this temperature was main- 5 l. A method forthe production of diborane which tained for a period of 12 hours. At theend of this comprises maintaining areactant consisting essentially ofreaction period the bomb was removed from the shaking at least onecompound of the class B(R) wherein R is apparatus, allowed to cool toroom temperature and an alkyl radical containing from one to .fivecarbon then vented through a trap maintained at 78 C. atoms in admixturewith hydrogen and in contact with a Gases passing through a -78 C. trapwere analyzed by catalyst selected from the group consisting of metalsof infrared and mass spectrograph and shown to be essenperiods 5 and dotgroup VIII of the periodic'table at tially diborane. The same testsshowed that a 70pera tfe'niper'ature within the range from 125 C. to 350C. cent Yield of dibofafle had been attained- Y examine" and aprssure offrom about 400 to 4000 p.s.i.g., and n of the material retained in the py infiai recovering diborane from the reaction mixture. red and massspectrographic methods it was shown that 15 2 The method f lai 1 wherein13 is trimethylthis product was essentially butane. b

A number of other experiments were completed in a 3. The method of claim1 wherein B(R) is triethylmanner similar to that described underExamples I, II bora and III and these experiments are set forth in TableI 4. The method of claim 1 wherein the catalyst is palbelow. ladium.

Table I Bomb Pres- Reaction Reaction Quantity of Trlalkylborane sure,p.s.i.g. Temp., Catalyst Time, Catalyst, Yield 0! Diborane C. hrs. mg.

(4) Trlethylborane 500 200 Palladium Black. 12 40 (based on Mass Spec.and IR Anal- (5) Alkylborane Trlethylhorane 2,000 200 Spongy Rhodlum 1250 O3 8 (l%. (6) Triothylborane 2,000 200 SpongyPlattuum..- 12 50 OverVarious changes can be made in the procedures described specificallyabove to provide other embodiments falling within the scope of thisinvention. Thus, in place of the palladium, rhodium and platinum metalcatalysts there can be substituted other metals of group VIII of theperiodic table, namely, iron, cobalt, nickel, ruthenium, osmium andiridium, and in place of the trirnethyl, triethyl and tri-n-butylboranes there can be substituted trin-propyl borane, tri-isobutylborane, tri-isoamyl. borane and so forth. The catalyst can be supportedon a carrier, if desired. The reaction temperature and pressure willgenerally be from C. to 350 C. (preferably C. to 250 C.) and from 400p.s.i.g. to 4000 p.s.i.g., al-

though temperatures and pressures above and below these 5. The method ofclaim 1 wherein the catalyst is platinum. 6 'Ihe method of claim 1wherein the catalyst is 35 rhodium.

- References Cited in the tile of this patent UNITED STATES PATENTS2,729,540 Fisher Ian. 3, 1956

1. A METHOD FOR THE PRODUCTION OF DIBORANE WHICH COMPRISES MAINTAINING AREACTANT CONSISTING ESSENTIALLY OF AT LEAST ONE COMPOUND OF THE CLASSB(R)3 WHEREIN R IS AN ALKYL RADICAL CONTAINING FROM ONE TO FIVE CARBONATOMS IN ADMIXTURE WITH HYDROGEN AND IN CONTACT WITH A CATALYST SELECTEDFROM THE GROUP CONSISTING OF METALS OF PERIODS 5 AND 6 OF GROUPS VIII OFTHE PERIODIC TABLE AT A TEMPERATURE WITHIN THE RANGE FROM 125*C TO350*C. AND A PRESSURE OF FROM ABOUT 400 TO 4000 P.S.I.G., AND RECOVERINGDIBORANE FROM THE REACTION MIXTURE.